Comb-form spectrum communication systems using repeated complementary sequence modulation

ABSTRACT

In comb-form spectrum communication systems using repeated complementary sequence modulation, a transmitting signal is constituted by assigning one set of N auto-complementary sequences to each user, where N is an integer equal to or higher than 2, and by transforming the N sequences to N repeated signals which have comb-form spectra without overlapping in frequency with one another with a method of repeating each sequence of the set of auto-complementary sequences a plurality of times, and by assigning the N complementary sequences with auto-complementary sequence characteristics to the N comb-form spectra. Thus, the near-far problem is solved by making the cross-correlation between a signal input to a user&#39;s station but addressed to another station and the user&#39;s reference code sequence, zero.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to comb-form spectrum communicationsystems using repeated complementary sequence modulation and relates to,in particular, means for solving the communication interruption causedby so-called near-far problem.

2. Description of the Background Art

In recent mobile communication systems such as a mobile telephone and aPHS (Personal Handyphone System), a Time Division Multiple Access (tobereferred to as ‘TDMA’ hereafter) system is adopted so as to provide anecessary channel capacity for the system. The TDMA system is designedin order to allow a plurality of users to share a predetermined,assigned frequency band, so that the time axis of the signal is dividedto thereby assign the divisions to users, respectively. The usablefrequency band is, however, limited and the number of time divisions isalso limited technically, for which reason the number of channels whichcan be assigned to users is limited, as well.

In recent years, as the user population of mobile communication systemsstated above increases, there has been proposed a Code Division MultipleAccess (to be referred to as ‘CDMA’ hereafter) system so as to providethe necessary channel capacity for the system. A CDMA system is designedin order to allow a plurality of users to share the same band, so thatthe users are identified with address spteading codes (inherent codes)assigned to them, respectively. Therefore, to facilitate theidentification of the inherent codes, the inherent codes are made on aclock frequency of higher than that of an information signal, forexample, two or three MH_(z). The information signal is multiplied bythe inherent codes to thereby increase the bandwidth of the transmissionsignal (or to spread the spectrum) and it is transmitted to atransmission path. Then, at a receiver, the correlation characteristicsof the received signal is obtained using matched filters etc. and theinherent codes are thereby demodulated. As stated above, since a CDMAsystem allows a plurality of users to share the same band, the number ofusers per bandwidth can probably increase compared with a TDMA system.Nevertheless, the problem of CDMA systems is that the number ofsimultaneous communication channels cannot increase due to theinterference that are the signals coming from other users which sharethe same band, and also due to the near-far problem which will bedescribed later.

FIG. 10 is a functional block diagram showing an example of theconstitution of a conventional CDMA system. In FIG. 10, four users areassumed. Since the following explanation will be given for a case whereinformation signals are transmitted from a user A to a user B and from auser D to a user C, respectively, the receivers of users A and D and thetransmitters of users B and C are not shown in FIG. 10.

In the CDMA system shown therein, each user possesses a transmitter 105(205) serving as a transmitting system and consisting of the firstmultiplier 102 (202) which multiplies an transmission information signala (b) outputted from a transmitting information generator 100 (200) bythe output signal of the first spreading code (PN code) generator 101(201) which generates inherent codes with a time width of Δt, assignedto respective users, and the second multiplier 104 (204) whichmultiplies the output signal of the first multiplier 102 (202) by theoutput carrier signal of the first local signal generator 103 (203).

Also, each user possesses a receiver 116 (216) serving as a receivingsystem and consisting of the third multiplier 112 (212) which multipliesa received signal 110 b (110 c) coming from a transmission path 110which takes a space as the medium, by the output signal of the secondlocal signal oscillator 111 (211), and a matched filter 115 (215) whichis composed of an integrator 114 (214) connected to the fourthmultiplier 113 (213) multiplying the output signal of the thirdmultiplier 112 (212) by the output signal of the second spreading code(PN code) generators 117 (217) generating the inherent code.

The required conditions for the above-described spreading codes are: (1)there are a lot of combinations of codes so that inherent codes can beassigned to a lot of users; (2) cross-correlation is so little that thecode of a user can be discriminated from that of another user; (3)auto-correlation to the same codes is impulsive so as to track thesignal addressed to the desired station and to facilitate thedemodulation; (4) a code is as random and long in length as possible toprevent the third party from eavesdropping the communications content,and so on. Generally, PN (pseudo-noise) codes are utilized as codessatisfying the above conditions.

Next, the operation of the CDMA system shown in this example will bedescribed. First, consider that user A who transmits an informationsignal a to user B. At the transmitter 105 of user A, the code generatedat the first PN code generator 101 is set to an inherent code Mbassigned to user B. The inherent code Mb is multiplied by theinformation signal a at the first multiplier 102 to thereby spread thespectrum, and the frequency of the resultant signal is transformed(modulated) to a transmission frequency by both the second multiplier104 and the first local carrier signal generator 103, and then theresultant output is sent out to the transmission path 110.

When receiver 116 of user B receives the said transmission signal, areceived signal 110 b is outputted to matched filter 115 after thefrequency is transformed (demodulated) by both oscillator 111 having thesame output frequency as the modulation frequency f0, and multiplier112. Matched filter 115 functions as a time correlator in terms ofoperational principle (for which detail, see, for example,“Communication System”, page 297, B. P. Lathi, translated in Japanese bySonosuke YAMANAKA and Koichi USAMI, McGraw-Hill Kogakusha, October 1981)and PN code generator 117 outputs the inherent code Mb assigned to theuser B's station. As a result, the output of the auto-correlationcharacteristics of the inherent code sequence Mb is produced frommatched filter 115.

FIG. 11 shows an example of the auto-correlation characteristics of thePN code which shows little correlation with a sequence shifted in phaseby more than one chip. Consequently, if the same code as the inherentcode assigned to the user B's station is inputted to the receiver, thematched filter produces the output of sharp auto-correlationcharacteristics, whereby the receiver can easily determine whether thereceived signal is addressed to the user B's station or not.

Now consider that an information signal b is transmitted from user D touser C while the information signal a is transmitted from user A to userB as stated above, the code of PN code generator 201 is set to aninherent code Mc assigned to user C at transmitter 205 of user D as inthe case of the transmission operation of transmitter 105 of user A. Theinherent code Mc is multiplied by the information signal b at multiplier202 to thereby spread the spectrum and, at the same time, the frequencyof the resultant signal is transformed (modulated) to a transmissionfrequency by both multiplier 204 and the output signal of local signalgenerator 203. Then the resultant transmission signal is transmitted totransmission path 110.

Accordingly, if receiver 216 of user C receives the signal transmittedfrom user D, PN code generator 212 outputs the inherent code Mc assignedto the user C's station as a spreading code. Thus, by performing thesame operation as that of receiver 116 of user B stated above, theoutput of the auto-correlation characteristics shown in FIG. 11 areproduced from matched filter 215. As a result, receiver 216 of user Crecognizes that the received signal is addressed to the user C'sstation.

Meanwhile, the signal spread by the PN code Mc transmitted fromtransmitter 205 of user D is also inputted to receiver 116 of user Bthrough transmission path 110. Consequently, the output of thecross-correlation characteristics between the inherent code Mc of user Cand the inherent code Mb of user B are produced from matched filter 115.

FIG. 12 shows the concept of the cross-correlation characteristics of PNcodes. The detail thereof is not described herein since it is describedin, for example, “Spectrum Spread Communication System”, pp. 406-409,Mitsuo YOKOYAMA, Kagaku-Gijutsu Publishing company, INC., 1988. Inshort, the cross-correlation characteristics between different PN codeshave various values according to the combinations of PN sequences and donot have fixed values as indicated by the auto-correlationcharacteristics shown in FIG. 11.

Therefore, matched filter 115 produces not only the output of theauto-correlation characteristics for detecting a signal addressed to theuser B's station shown in FIG. 11, but also unnecessary output of thecross-correlation characteristics shown in FIG. 12. Generally, thecross-correlation characteristics among inherent codes such as Mb and Mcassigned to respective users are designed to take levels sufficientlylower than those of the auto-correlation characteristics, by making thecodes not similar to one another.

Nonetheless, the conventional CDMA system using PN codes as spreadingcodes stated above has the following major problems. Since each userfreely moves in mobile communication, there are some cases where thesignal (interference wave) level (cross-correlation characteristicsshown in FIG. 12) inputted to a user's receiver but addressed to adifferent station is higher than that (the auto-correlationcharacteristics shown in FIG. 11) addressed to the user's station,depending on the user's position. This is a well-known problem called‘near-far problem’. If the problem occurs, the signal addressed to theuser's station is masked by the interference wave and cannot bedetected. Furthermore, communication disturbance occurs, such as causedby multi-path signals due to reflection waves which disturbs receiverdetecting operation similarly to the interference waves.

To avoid the near-far problem, it is essential to appropriately controlthe transmission power levels of the respective transmitters in theoverall system in accordance with the movement of the users. It has beendisadvantageous that the power control makes the system constitutioncomplicate and large in size.

The present invention has been made to solve the above-stated problemson the conventional CDMA communication systems. The invention is to makethe matched filter output level (the cross-correlation characteristicsbetween the interference wave and a desired station signal) zero when aninterference wave is given to the input to thereby solve the near-farproblem. It is, therefore, an object of the present invention is toprovide a CDMA communication system which is composed of a simpleconstitution because it does not require the transmission power controlof the respective transmitters, and is easily equipped with multi-pathsignal separation function.

SUMMARY OF THE INVENTION

To achieve the above object, a first aspect of the present invention iscomb-form spectrum communication systems using repeated complementarysequence modulation wherein a transmitting signal is constituted byassigning one set of N auto-complementary sequences to each user, whereN is an integer equal to or higher than 2, and by transforming said Nsequences to N repeated signals which have comb-form spectra withoutoverlapping in frequency with one another with a method of repeating oneof said auto-complementary sequences a plurality of times, and byassigning said N complementary sequences with auto-complementarysequence characteristics to said N comb-form spectra.

A second aspect of the invention is comb-form spectrum communicationsystems using repeated complementary sequence modulation based on thecomb-form spectrum communication systems using repeated complementarysequence modulation according to the first aspect, wherein saidtransmitting signal is constituted by preparing N shift carrier waves sothat the K-th frequency is made by adding the inverted value f_(T) of asymbol period T K-times to a reference frequency so as to prevent said Ncomb-form spectra from overlapping with one another, where K=0, 1, 2, .. . , N−1, and by composing N signals each created by modulating saidrespective N shift carrier waves with repeated sequences which are madeby repeating respective sequences of each set of N complementarysequences which have a relation of auto-complementary sequences.

A third aspect of the invention is comb-form spectrum communicationsystems using repeated complementary sequence modulation based on thecomb-form spectrum communication systems using repeated complementarysequence modulation according to the first aspect, wherein said set of Nauto-complementary sequences assigned to each user are constituted sothat said set of N auto-complementary sequences assigned to each user iscross-complementary to a set of N auto-complementary sequences assignedto another user; and the carrier waves used by all the users are said Nshift carrier waves.

A fourth aspect of the invention is comb-form spectrum communicationsystems using repeated complementary sequence modulation based on thecomb-form spectrum communication systems using repeated complementarysequence modulation according to the second aspect, wherein for a casewhere said set of auto-complementary sequences assigned to each user arenot cross-complementary to a set of sequences assigned to another user,said transmitting signals are constituted so that the complementarysequences assigned to each user modulate said shift carrier waves whosefrequencies are different from those used by the other users.

A fifth aspect of the invention is comb-form spectrum communicationsystems using repeated complementary sequence modulation based on thecomb-form spectrum communication systems using repeated complementarysequence modulation according to one of the first to fourth aspects,wherein at a receiver side of the system, N matched filters each matchedto a part of a code made by repeating each sequence of said set of Nauto-complementary sequences are arranged in parallel in accordance withsaid set of N auto-complementary sequences, and the transmittedinformation is detected based on a result obtained by adding thecorrelation outputs of said N matched filters.

A sixth aspect of the invention is comb-form spectrum communicationsystems using repeated complementary sequence modulation based on thecomb-form spectrum communication systems using repeated complementarysequence modulation according to one of the first to fourth aspects,wherein pseudo-periodic sequences, such as obtained by copying the rearand front portions with multiple chips of a finite-length periodicsequence which is made by repeating each sequence of said set of Nauto-complementary sequences, and thereby adding the copied portions tothe outer front side and the outer rear side of said finite lengthperiodic sequence respectively, are used as codes assigned to respectiveusers; and matched filters, each matched to said finite length periodicsequence made before extending itself to said pseudo-frequency sequence,are used for demodulation at the receiver side.

A seventh aspect of the invention is comb-form spectrum communicationsystems using repeated complementary sequence modulation whereincorrelation outputs are obtained by using convolvers instead of saidmatched filters according to one of the fifth and sixth aspects.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram showing the first embodiment of aCDMA communication system according to the present invention;

FIG. 2 is a frequency spectrum illustration for a case of modulating acarrier wave of f0 by a sequence constituted by repeating anauto-complementary sequence (A0) twice;

FIG. 3 is a frequency spectrum illustration for a case of modulating acarrier wave of f1 by a sequence constituted by repeating anauto-complementary sequence (A1) twice;

FIG. 4 is a model for explaining the concept of a multi-path signalgeneration;

FIG. 5 shows the auto-correlation characteristics of a multi-pathsignal;

FIG. 6 shows the relation between code sequences assigned to respectiveusers and their frequency spectra in the first embodiment of the CDMAcommunication system according to the present invention;

FIG. 7 shows a spectrum in a case where a spreading code waveform(baseband) using a square wave is repeated infinitely;

FIG. 8 shows the relation between code sequences assigned to respectiveusers and their frequency spectrum in the second embodiment of the CDMAcommunication system according to the present invention;

FIG. 9 shows examples of the frame constitution of signals;

FIG. 10 is a functional block diagram showing an example of theconstitution of a conventional CDMA communication system;

FIG. 11 shows an example of the auto-correlation characteristics of a7-bit PN code; and

FIG. 12 shows the concept of the cross-correlation characteristics of PNcodes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, the present invention will be described in detail based on theembodiments shown in the drawings.

FIG. 1 is a functional block diagram showing the first embodiment in acase where the communication system according to the present inventionis applied to a CDMA communication system. In FIG. 1, it is assumed thatthere are four system users. As in the case of the description of“Background of Art”, description will be given to a case whereinformation signals are transmitted from a user A to a user B and a userD to a user C, respectively. Therefore, the description on the receiversof users A and D as well as the transmitters of users B and C areomitted.

In addition, N auto-complementary sequences (where N is an integer equalto or higher than 2), which will be described later, used as inherentcodes can be assigned to each user. For brevity's sake, description willbe given to a case where N=2, i.e., a pair of auto-complementarysequences are used by each user.

In a CDMA communication system shown in this example, each userpossesses a transmitter 1 (2) serving as a transmitting system andconsisting of the first pair of multipliers 12α, 12β (22α, 22β) whichmultiply the output signals of a transmitting information generator 10(20) outputting transmitting information a (b) by the output signals ofa pair generators 11α, 11β (21α, 21β). The respective generatorsgenerate a pair of auto-complementary sequences as the first spreadingcodes which are the pair of inherent codes assigned to each user. Andthe first adder 15 (25) adds the outputs of the second pair ofmultipliers (mixers) 14α, 14β (24α, 24β) which multiply the outputsignals of the first multipliers 12α, 12β (22α, 22β) by the outputsignals of the first pair of local signal generators 13α, 13β (23α,23β).

Each receiver also possesses a receiver 3 (4) serving as a receivingsystem and consisting of a pair of matched filters 32α, 32β (42α, 42β)connected to the third pair of multipliers (mixers) 31α, 31β (41α, 41β).These mixers multiply a received signal 19 a (19 b) which is conveyedthrough a transmission path 19 by the output signals of the second pairof local signal oscillators 30α, 30β (40α, 40β). And the second adder 33(43) adds the outputs of matched filters 32α, 32β (42α, 42β). Thedetailed functional block diagram of matched filters 32α, 32β (42α, 42β)are not shown in FIG. 1. However, they are the same as a conventionalfilter functioning as a time correlator equipped with both a multipliermultiplying an input signal by the output signal of the second codegenerator which generates an inherent code (one of the pair ofauto-complementary sequence) assigned in advance to each user and anintegrator connected to the multiplier.

The same correlation outputs as those of matched filters 32α, 32β, 42α,42β can be obtained even if the filters are replaced by convolvers. Inthat case, the reference input of, for example, a convolver used as 32αis a sequence A0A0 to be stated later.

Prior to starting the description of the function of the CDMAcommunication system shown in this example, the correlationcharacteristics of the auto-complementary sequences used as spreadingcodes (inherent codes) characterizing the present invention and thefrequency spectrum characteristics of the codes constituted by repeatingeach of auto-complementary sequences will be described in detail.

First, by way of example, the following eight-chip code sequences aretaken:A0=(1, 1, 1, −1, 1, 1, −1, 1)  (1)A1=(1, −1, 1, 1, 1, −1, −1, −1)  (2)B0=(1, 1, 1, −1, −1, −1, 1, −1)  (3)B0=(1, −1, 1, 1, −1, 1, 1, 1)  (4).The aperiodic auto-correlation function of A0 is obtained as:A0*A0=(1, 0, 1, 0, 3, 0, −1, 8, −1, 0, 3, −0, 1, 0, 1)  (5).The aperiodic auto-correlation function of A1 is obtained as:A1*A1=(−1, 0, −1, 0, −3, 0, 1, 8, 1, 0, −3, 0, −1, 0, −1)  (6).The sum of the auto-correlation functions of A0 and A1 is:A0*A0+A1*A1=(0, 0, 0, 0, 0, 0, 0, 16, 0, 0, 0, 0, 0, 0, 0)  (7).Thus, a sequence which does not have a side lobe except at the centralshift in chip is obtained. {A0, A1} is referred to as auto-complementarysequences.

Likewise, the auto-correlation functions of B0 and B1 are obtained andthe sum of them is obtained as follows:B0*B0=(−1, 0, −1, 0, −3, 0, 1, 8, 1, 0, −3, 0, −1, 0, −1)  (8)B1*B1=(1, 0, 1, 0, 3, 0, 0, −1, 8, −1, 0, 3, 0, 1, 0, 1)  (9)B0*B0+B1*B1=(0, 0, 0, 0, 0, 0, 0, 16, 0, 0, 0, 0, 0, 0, 0)  (10).Thus, {B0, B1} is auto-complementary sequences, as well.

Further, if sequence A0 in Eq. (1) is applied to the matched filter ofthe reference sequence B0 expressed by Eq. (3), the matched filterfunctions as a time correlator as stated above, and thecross-correlation function between A0 and B0 is obtained at the outputterminal of said matched filter as follows:A0*B0=(−1, 0, −1, 0, −5, 0, 3, 0, 1, 0, 1, 0, 1, 0, 1)  (11).

Likewise, if the sequence A1 is applied to the matched filter of thereference sequence B1, the cross-correlation function between A1 and B1is obtained at the output terminal of the matched filter as follows:A1*B1=(1, 0, 1, 0, 5, 0, −3, 0, −1, 0, −1, 0, −1, 0, −1)  (12).Consequently, the sum of the Eqs. (11) and (12) is:A0*B0+A1*B1=(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0)  (13).

On the contrary, if sequence B0 expressed by Eq. (3) is applied to thematched filter of the reference sequence A0 expressed by Eq. (1), thecross-correlation function between B0 and A0 is obtained at the outputterminal of the matched filter as follows:B0*A0=(1, 0, 1, 0, 1, 0, 1, 0, 3, 0, −5, 0, −1, 0, −1)  (14).If sequence B1 expressed by Eq. (4) is applied to the matched filter ofthe reference sequence A1 expressed by Eq. (2), the cross-correlationfunction between B1 and A1 is obtained at the output of the matchedfilter as follows:B1*A1=(−1, 0, −1, 0, −1, 0, −1, 0, −3, 0, 5, 0, 1, 0, 1)  (15).Consequently, the sum of Eqs. (14) and (15) is:B0*A0+B1*A1=(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0)  (16).

That is, when the pairs of auto-complementary sequences, {A0, A1} and{B0, B1}, are applied to pairs of matched filters of respectivecounterpart reference sequences, respectively, and the outputs of eachpair of the matched filters are added, the resultant cross-correlationfunction becomes zero as expressed by Eq. (13) or (16). Combinationsequences {A0, A1} and {B0, B1} having the above characteristic relationare referred to as cross-complementary sequences. Further, ifcombination sequences {A0, A1} and {B0, B1} are pairs ofauto-complementary sequences, [{A0, A1} and {B0, B1}] are referred to asa set of complete complementary sequences.

Now, the frequency spectrum of waveforms in a case where a basicsequence A0 is repeated at every time interval of the frame period Twill be described.

If it is assumed that L0 is number of chips/sequence, the length ofsequence A0 is given as T=L0Δt0. The spectrum of a periodic basebandsignal in which the impulse-sequence is repeated at every interval of Tsecond, is a basic spectrum which consists of such elements of aninteger multiple of f_(T) over −fc0/2˜0˜fc0/2 as obtained by DFT(discrete Fourier transform) analysis, where fc0=1/Δt0 and f_(T)=1/T.That is, the baseband signal has a spectrum centered around f=0 andcontaining components in k·f_(T) (where k=−∞˜−2, −1, 0, 1, 2, ˜∞).

Actually, however, impulse transmission is impossible. If, for example,a square wave having a time width of Δt0 is used instead of the impulse,the spectrum of the square wave is approximately expressed as a spectrumranging from -fc0˜0˜fc0, where 90% or more of the signal energy iscontained.

The components contained other than (−fc0˜0˜fc0) are out-of-bandcomponents. The spectrum of a signal which is made by repeatinginfinitely a baseband waveform which is a sequence with square waves ofa code length of L0=8 in a frame period T, is obtained by DFT analysisas shown in FIG. 7. The spectrum amplitude at f=±fc0 disappears, in thefigure, because this frequency coincides with the point on which thesampling function takes zero and it shows the amplitude characteristicsin which the amplitudes gradually decrease so as to take the envelope ofthe sampling function on both sides of f=0.

Now, let us describe the frequency spectrum of a code made by repeatingthe auto-complementary sequence stated above a plurality of times. Acode made by repeating the sequence A0 stated above twice is expressedas:A0A0=(1, 1, 1, −1, 1, 1, −1, 1, 1, 1, 1, −1, 1, 1, −1, 1)  (17)Due to the periodicity of repeating the sequence twice, the frequencyspectrum takes such a comb-form spectrum that some possible frequencycomponents are lost. If two basic sequences are included in T, T=LΔt andL=2L0=16, then Δt=At0/2 and, therefore, fc=1/Δt=2fc0. Thus, the occupiedbandwidth is doubled but the spectrum at kf_(T) (where k is an oddnumber) takes zero. The comb-form spectrum, however, overlaps with thatof the other code made by repeating the other sequence A1 twice (A1A1)which will be described later. However, it is possible to use them byshifting their frequencies each other.

FIG. 2 shows the positive frequency portion of a spectrum in a casewhere f0 is modulated by a signal having this spectrum by means ofDSB-AM (double side band amplitude modulation) (in the figure, thenegative frequency components and out-of-band components are not shownand the amplitude decreasing characteristics based on a square wave isnot shown, either). Since the basic sequence is repeated twice and thepulse width is halved, it results in fc=2fc0 and making the amplitude ata frequency of k·f_(T) (where k is an odd number) zero.

Meanwhile, a code constituted by repeating, as stated above, thesequence A1 twice is expressed as:A1A1=(1, −1, 1, 1, 1, −1, −1, −1, 1, −1, 1, 1, 1, −1, −1, −1)  (18).The frequency spectrum of this code takes the same comb-form spectrum asshown in FIG. 2. FIG. 3 shows the frequency spectrum of a signal whichis composed by modulating (for frequency transform) a shift carrier waveof a frequency f1=f0+f_(T) with the code sequence expressed by Eq. (18).In this case, f_(T)=1/T and the frequency f1 is selected so that thespectra shown in FIGS. 2 and 3 may be interleaved.

Consequently, the signals shown in FIGS. 2 and 3, i.e., the codesexpressed by Eqs. (17) and (18) not only have mutually interleavedspectra but also their spectra are distant from each other by an integertimes f_(T)=1/T. Hence, they have such orthogonal character that theymay not interfere with each other even if they would be simultaneouslytransmitted under the conditions to be stated later.

The orthogonality stated above also holds true for the relation betweena code sequence B0B0 made by repeating B0 and a code sequence B1B1 madeby repeating B1 because of the same logic as described above.

In short, only if a plurality of codes belong to pairs ofauto-complementary sequences which have the relation ofcross-complementary sequences among the pairs, the sum of respectivecross-correlation functions between a pair of sequences and thecorresponding sequences of another pair have level zero characteristics(no-correlation characteristics). In addition, since code sequences madeby repeating a sequence a plurality of times, form vacant components inspectrum, these codes can be simultaneously transmitted by using meansof setting the frequencies of the carrier waves so as not to overlaptheir spectra with each other.

In the above description, explained were the correlation characteristicswith respect to both auto-complementary sequences andcross-complementary sequences, and in addition, the frequencycharacteristics with a vacant spectrum of a code made by repeating eachsequence of a pair of auto-complementary sequences a plurality of times.These characteristics are the notable features of the present invention,and were explained to describe the operation on the CDMA communicationsystem taken as the first embodiment example shown in FIG. 1. Let us nowexplain the operation of the CDMA communication system shown in FIG. 1,while taking account of the characteristics of the codes which consistsof a pair of auto-complementary sequences as stated above.

As an example of inherent codes assigned to each user, let us explain acase where codes made by repeating each sequence of a pair of theauto-complementary sequences given by Eqs. (1) to (4) four times areused. Thus, each code has 32 chips in length and is also viewed as apseudo-periodic sequence having demodulation period with 16 chips.Therefore, by setting shift carrier waves f0 and f1 to have f0+kf_(T)(where K=0, 1, 2, . . . , N−1), the respective codes composed of a pairof auto-complementary sequences can be simultaneously transmitted,because their spectra do not overlap with one another.

First, in order to transmit an information signal a from user A to userB, sequences produced from the first pair of auto-complementary sequencegenerators 11α and 11β accomodated in transmitter 1 of user A are set tobe inherent codes A0A0A0A0 and A1A1A1A1, respectively, which areassigned to user B.

Transmitted to a transmission path 19 a transmitting signal which isproduced by such a method that the inherent codes are multiplied by theinformation signal a at the first pair of multipliers 12α, 12β,respectively, to thereby spread the spectrum, and then the spreadoutputs are frequency-transformed (modulated) with transmitting shiftcarrier wave frequencies f0 and f1 which are supplied by the first pairof local oscillators 13α, 13β, respectively, at the second pair ofmultipliers 14α, 14β and the frequency shifted outputs thereof are addedtogether at adder 15 to make the transmitting signal. In this process,transmitting carrier wave frequencies f0 and f1(=f0+f_(T)) are designedso that codes A0A0A0A0 and A1A1A1A1 may have spectra which do notoverlap with each other based on the pseudo-periodic sequence propertiesstated above. For this reason, when these signals are transmittedsimultaneously and they are correlatively detected for T seconds at thereceiver side, there is no inter-code interference occurs, because thefrequency components of these signals are orthogonal to each other.

If receiver 3 of user B receives the transmitted signal from user A, thesignal is frequency-transformed (demodulated) by carrier waves offrequencies f0 and f1 supplied from the second pair of local oscillators30α, 30β, respectively, at the third pair of multipliers 31α, 31β, andthe transformed outputs are applied to a pair of matched filters 32α,32β, respectively. Since matched filters 32α, 32β function as timecorrelators as stated above, they produce the correlation function withthe input codes.

Here, to explain quantitatively the correlation characteristics, theabove-stated modulation and demodulation signals are expressed bynumeric equations. First, code A0A0A0A0 is modulated by frequency f0 anddemodulated by frequency f0, then code A0A0A0A0 is obtained again. Bycontrast, if code A0A0A0A0 is modulated by frequency f0 and demodulatedby frequency f1, an output expressed by the following equation isobtained:(A0A0)_(f0, f1)(A0A0)_(f0, f1)  (19).Also, if code A1A1A1A1 is modulated by frequency f1 and demodulated byfrequency f0, an output expressed by the following equation is obtained:(A1A1)_(f1, f0)(A1A1)_(f1, f0)  (20).If code A1A1A1A1 is modulated by frequency f1 and demodulated byfrequency f1, code A1A1A1A1 is obtained again.

Then, if A0 is applied to the matched filter matched to A0, the filteroutputs:A0*A0=(1, 0, 1, 0, 3, 0, −1, 8, −1, 0, 3, 0, 1, 0, 1)  (5),as described above. Thus, if A0 is applied to the matched filter matchedto A0A0, used by the receiver of user B shown in FIG. 1, then thematched filter outputs:A0*A0A0=(1, 0, 1, 0, 3, 0, −1, 8, 0, 0, 4, 0, 4, 0, 0, 8, −1, 0, 3, 0,1, 0, 1)  (21)based on the same processing as given by Eq. (5). Therefore, if codeA0A0A0A demodulated by frequency f0 is applied to the matched filtermatched to A0A0, where the receiver of user B shown in FIG. 1 isassumed, the matched filter outputs the auto-correlation characteristicsindicated as follows:A0A0A0A0*A0A0=(1, 0, 1, 0, 3, 0, −1, 8, 1, 0, 5, 0, 7, 0, −1, 16, 0, 0,8, 0, 8, 0, 0, 16, 0, 0, 8,0,8, 0, 0, 16, −1, 0, 7, 0, 5, 0, 1, 8, −1,0, 3, 0, 1, 0, 1)  (22).

Then, if code A1A1A1A1 modulated by frequency f1 and demodulated byfrequency f0, i.e., signal (A1A1)_(f1, f0)(A1A1)_(f1, f0) expressed byEq. (20) is applied to the matched filter matched to A0A0, the matchedfilter outputs the cross-correlation characteristics as follows:(A1A1)_(f1, f0)(A1A1)_(f1, f0) *A0A0=(p15, p14, p13, p12, p11, p10, p9, p8,p7, p6, p5, p4, p3, p2, p1, 0, 0, 0, 0, 0, 0, 0, 0,0, 0, 0, 0, 0, 0, 0, 0, q1, q2, q3, q4, q5, q6, q7,q8, q9, q10, q11, q12, q13, q14, q15)  (23).Here, pi, qj take numeric values other than zero in accordance with thecode sequences (or may take zero accidentally). Therefore, even if codeA1A1A1A1 is applied to the matched filter matched to A0A0 as indicatedby Eq. (23), the components take zero on the shift range from shifted tothe left by −8 chips, to shifted to the right by +8 chips around thecentral shift in chip. In the shift range the auto-correlationcharacteristics indicated by Eq. (22) is not influenced.

In addition, if code A1A1A1A1 is applied to the matched filter matchedto A1A1, the filter outputs the following auto-correlationcharacteristics as in the case of Eq. (22):A1A1A1A1*A1A1=(−1, 0, −1, 0, −3, 0, 1, 8, −1, 0, −5, 0, −7, 0, 1, 16, 0,0, −8, 0, −8, 0, 0, 16, 0, 0, −8, 0, −8, 0, 0, 16, 1, 0, −7, 0, −5, 0,−1, 8, 1, 0, −3, 0, −1, 0, −1)  (24).

Furthermore, if code A0A0A0A0 modulated by frequency f0 and demodulatedby frequency f1, i.e., the signal (A0A0)_(f0, f1)(A0A0)_(f0, f1)indicated by Eq. (19) is applied to the matched filter matched to A1A1,then the filter outputs the following cross-correlation characteristicsobtained by the same processing as that of Eq. (23):(A0A0)_(f0, f1)(A0A0)_(f0, f1) *A1A1=(r15, r14, r13, r12, r11, r10, r9, r8,r7,r6, r5, r4, r3, r2, r1, 0, 0, 0, 0, 0, 0, 0, 0,0, 0, 0, 0, 0, 0, 0, 0, 0, s1, s2, s3, s4, s5, s6, s7,s8, s9, s10, s11, s12, s13, s14, s15)  (25).Here, ri, sj take numeric values other than zero in accordance with thecode sequences as in the case of pi and qj; however, the components takezero on the shift range from shifted to the left by −8 to shifted to theright by +8 around the central shift. Therefore, similarly to the caseof Eq. (23), Eq. (25) does not influence the auto-correlationcharacteristics indicated by Eq. (24) in this range.

Accordingly, a signal obtained by adding code A0A0A0A0 multiplied by thetransmitting information a and then modulated by f0, and code A1A1A1A1multiplied by the transmitting information a and then modulated by f1 isexpressed by:a{(A0A0)_(f0)(A0A0)_(f0)+(A1A1)_(f1)(A1A1)_(f1)}  (26).If the signal is demodulated by frequencies f0 and f1, respectively, atthe receiver of user B, the signal demodulated by frequency f0 isexpressed by:a{(A0A0)_(f0, f0)(A0A0)_(f0, f0)+(A1A1)_(f1, f0)(A1A1)_(f1, f0)}  (27),and the signal demodulated by frequency f1 is expressed by:a{(A0A0)_(f0, f1)(A0A0)_(f0, f1)+(A1A1)_(f1, f1)(A1A1)_(f1, f1})  (28).

If the signal demodulated by frequency f0 as indicated by Eq. (27) isapplied to the matched filter matched to A0A0 and the signal demodulatedby frequency f1 as indicated by Eq. (28) is applied to the matchedfilter matched to A1A1, and the outputs of both the matched filters areadded together at the second adder 33, the result is:a{(A0A0)_(f0, f0)(A0A0)_(f0, f0)+(A1A1)_(f1, f)₀(A1A1)_(f1, f0)}*A0A0+a{(A0A0)_(f0, f1)(A0A0)_(f0, f1)+(A1A1)_(f1, f1)(A1A1)_(f1, f1)}*A1A1  (29).If Eqs. (22) and (23) are applied to the upper stage and Eqs. (25) and(24) are applied to the lower stage in Eq. (29), the result is:a(p15+r15, p14+r14, p13+r13, . . . , p3+r3, p2+r2, p1+r1, 32, 0, 0, 0,0, 0, 0, 0, 32, 0, 0, 0, 0, 0, 0, 0, 32, q1+s1, q2+s2, q3+s3, . . . ,q13+s13, q14+s14, q15+s15)  (30).Thus, in the shift range from shifted to the left by −7 to shifted tothe left by −1 and that from shifted to the right by +1 to shifted tothe right by +7 around the central shift (indicated by 32 in value), theoutput can provide sharp auto-correlation characteristics without a sidelobe, whereby it is possible to easily determine that the receivedsignal is of self-addressed.

On the other hand, in parallel with the transmission of an informationsignal a from user A to user B by means of [A0, A1], an informationsignal b should be transmitted from user D to user C by the same methodsuch as using a pair of auto-complementary sequences [B0, B1] andcarrier waves with the same frequencies f0 and f1 as stated above. Forthis purpose, let us consider a frequency arrangement (shown in theright side of f0, f1) shown in FIG. 6. In this system, a signal [B0, B1]is mixed into the receiver 3 of user B as an interference wave. Theoperation will be quantitatively described herein after. If a spreadingcode B0B0B0B0 is multiplied by the information signal b and modulated byfrequency f0 at receiver 2 of user D by the same processing as thatcarried out at transmitter 1 of user A, another spreading code B1B1B1B1is multiplied by the same information b and modulated by a frequency f1and the both signals are added together and transmitted, then the resultis:b{(B0B0)_(f0)(B0B0)_(f0)+(B1B1)_(f1)(B1B1)_(f1)}  (31).Then the resultant signal given by Eq. (3) is demodulated by frequenciesf0 and f1, respectively at receiver 3 of user B. A part of thedemodulated output which is demodulated by frequency f0 is expressed asfollows:b{(B0B0)_(f0, f0)(B0B0)_(f0, f0)+(B1B1)_(f1, f0)(B1B1)_(f1, f0)}  (32)and the other output which is demodulated by frequency f1 is expressedas follows:b{(B0B0)_(f0, f1)(B0B0)_(f0, f1)+(B1B1)_(f1, f1)(B1B1)_(f1, f1)}  (33).

The signal demodulated by frequency f0 given by Eq. (32) and thatdemodulated by frequency f1 given by Eq. (33) are applied to the matchedfilters matched to A0A0 and A1A1, respectively. Then, by adding theoutputs of both the matched filters together, the result is obtainedsimilarly to the case of Eq. (29):b{(B0B0)_(f0, f0)(B0B0)_(f0, f0)+(B1B1)_(f1, f0)(B1B1)_(f1, f1)}*A0A0+b{(B0B0)_(f0, f1)(B0B0)_(f0, f1)+(B1B1)_(f1, f1)(B1B1)_(f1, f1)}*A1A1  (34).If the same processing as that used for deriving Eq. (30) from Eq. (29)is applied, the result of Eq. (34) is expressed by:b(p15′+r15′, p14′+r14′, p13′+r13′, . . . ,p3′+r3′, p2′+r2′, p1′+r1′, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,0, 0, 0, 0, 0, 0, q1′+s1′, q2′+s2′, q3′+s3′, . . . ,q13′+s13′, q14′+s14′, q15′+s15′,)  (35).Thus, the components takes zero on the shift range from shifted to theleft by −8 to shifted to the right by +8 around the central shift.

Consequently, when user B decides that the signal [A0, A1] transmittedfrom user A is one of the self-addressed signals, based on thecorrelation values in the shift range from shifted to the left by −7 toshifted to the right by +7, even if the signal [B0, B1] transmitted fromanother station (user D) is mixed into receiver 3 of user B, the signal[B0, B1] does not disturb the decision of the self-addressed signalcarried out based on Eq. (30). This is because the correlation due to[B0, B1] takes zero in the shift range from shifted to the left by −8 toshifted to the right by +8 as indicated by Eq. (35). This is achieved bydesigning so that sequences [A0, A1] and [B0, B1] may take the relationof cross-complementary sequences despite they use the same band{(f0−1/Δt)˜(f1+1/Δt)}.

Therefore, in the CDMA communication system according to the presentinvention, in the time period of auto-correlation characteristics when auser decides whether a signal is of self-addressed or not, thecorrelation characteristics with a mixed signal addressed to a differentstation take zero without fail, therefore, no near-far problem will takeplace. This problem takes place for conventional systems due to thepositional relation among the respective users. As a result, thetransmission power control for each transmitter to be performedfollowing to the movement of each user will not required. Thereby it ispossible to make the system quite simple.

Furthermore, by utilizing such characteristics that the correlation withthe signal coming from another station takes zero, the CDMAcommunication system according to the present invention is capable ofeasily separating the multi-path signals which occur for urban areamobile communications. FIG. 4 is an illustration showing the concept asto how a multi-path signal generates. A transmitting signal sent outfrom a transmitter 41 is separated into a direct signal 43 directlyreaching a receiver 42 and a multi-path signal (reflection signal) 45reflected by a reflector 44 and then reaching receiver 42. If multi-pathsignal 45 reaches receiver 42 at the same level as that of direct signal43, the same-level signals having phases shifted each other are input toreceiver 42. This causes a waveform distortion or the like to therebydeteriorate the reception performance of receiver 42.

FIG. 5 shows the auto-correlation characteristics observed at the outputof the second adder 33 (43) shown in FIG. 1 in a case where multi-pathsignal 45 is input to the receiver. As stated above, theauto-correlation characteristics do not have a side lobe in the shiftrange from shifted to the left by −7 to shifted to the right by +7around the central shift. Therefore, it is possible to separate thedirect signal (indicated by solid line) from the multi-path signal(indicated by dotted line) expressed by Eq. (30) due to the phase-shift(time-delay or TM to be described later). The position of the centralshift is clarified by synchronization established for the receivedsignals on the received wave. Consequently, if the delay time betweenthe direct wave and the delay wave is denoted by τd=τM−τ0 and the codelengths of basic sequences A0 and A1 denoted by L0, then it is possibleto ensure separating the multi-path signal as long as TM=L0Δt−τd>0.

The system according to the present invention is constructed under theassumption that the incoming phase of an interference wave coincideswith that of a desired wave. If a phase difference exists and theboundary of the frame of the interference signal υB is within the frameof the desired signal υA as shown in FIG. 9, then a correlation due tothe interference occurs, because υB may be different from the assumedsignals described above. This is caused by the fact that υB is modulatedby the information b in frame by frame basis.

Although it is actually difficult to synchronize the frame phase of theinterference signal with that of the desired signal. However, thecontrol technique which keeps the time difference within τdif shown inthe figure has been realized in TDMA mobile communication systems. If itis assumed that the quasi-synchronizing technique is used, and thetransmitting signals {overscore (υA)} and {overscore (υB)} are made soas to have extended frame lengths (pseudo-period) TE longer than theframe length TDEM used for demodulating correlation of a received signalwhere the receiving time difference τdif between their frames may takeso as to be τdif<TA, then only interference waves which are notmodulated enter into the demodulation time TDEM of υA, therefore, nocorrelation caused by {overscore (υB)} occurs. The extended frame of{overscore (υA)} is formed by adding a tail portion and a front portionof υA to the outer front side and the outer rear side of υA,respectively. FIG. 9 shows a simple example of a case where theconstituent element A0 of υA is added to the front and rear portions.

Consider a case where one user uses two transmitters and the other useruses two receivers. For example, one user uses transmitters 1 and 2 andthe other user uses receivers 3 and 4 shown in FIG. 1. Thus, one usercan simultaneously transmit the transmitting information a and b, withthe result that the advantage of doubling transmission speed can beobtained.

In the first embodiment according to the present invention which hasbeen described so far, the system is constructed so that the correlationvalues of a signal mixed into a user's station and addressed to anotherstation may take zero by assigning the common carrier wave frequenciesf0 and f1 which are different to respective users and by assigningspreading codes which are mutually cross-complementary sequences, torespective users. Therefore, if the number of combinations ofcomplementary sequences is m, it is possible to realize m simultaneouscommunications using almost the same band without causingcross-interference. To carry out the present invention, it should be notnecessary to limit the first embodiment. In the second embodimentdescribed hereinafter, for example, spreading codes assigned to eachuser are the same auto-complementary sequences as used in the firstembodiment. However, it can be a frequency division multiple accesssystem such that the codes assigned to each user are notcross-complementary sequences and that carrier waves used for therespective users may have different frequencies.

FIG. 6 shows the relation between codes and spectra in a case where thesystem constitution in the first embodiment shown in FIG. 1 is used.Specifically, it shows the relation between pairs of codes each made byrepeating each sequence of a pair of auto-complementary sequencesassigned to each user to which the signals are transmitted and theirspectra, for a case where two users (A, D) amoung four users transmitinformation signals, respectively. To simplify the illustration of thespectra, it is assumed that each auto-complementary sequence is made byrepeating a 8-chip basic sequence four times. For example, it is assumedthat A0 in Eq. (1) and A1 in Eq. (2) are provided for transmission (A toB). The spectra of the outputs obtained by modulating (f0, f1) withthese repetitive codes, respectively are shown in the upper part of FIG.6.

Unlike FIG. 8 to be described later, FIG. 6 shows a case where a set ofB0 in Eq. (3) and B1 in Eq. (4) which have the relation ofcross-complementary sequences with respect to the set of A0 and A1,respectively are used for another transmission (D to C). The spectra ofoutputs obtained by modulating(f0, f1) with B0 and B1, respectively areshown in the lower part of FIG. 6. Codes A0 and B0 produce transmissionwaves by modulating carrier wave f0, whereas codes A1 and B1 producetransmission waves by modulating carrier wave f1. The spectra of thecarrier waves for transmission from A to B coincide with these of thecarrier waves for transmission from D to C as shown in FIG. 6. Due tothe relation of cross-complementary sequences, no interference occurs atthe receiver side. As for other transmissions (B to A) and (C to D),repetitive code sequences of (A0, A1) and (B0, B1) may be used,respectively and transmission waves are produced by the same methodusing carrier waves different from f0 and f1, i.e.,f2=f1+f _(T)f3=f2+f _(T).In this case, the same carrier waves are used for transmissions from Bto A and from C to D. Although the spectra of the transmission waves inthis case are not shown in FIG. 6, they are arranged in the vacantspectra shown therein, so that no interference with transmission waves(A to B) and (D to C) occurs. Therefore, the band occupied by the systemin the first embodiment is advantageously halved compared to the bandoccupied by the case of FIG. 8. If the number of sets ofcross-complementary sequences are used, frequency utilization efficiencyfurther enhances.

FIG. 8 shows the relation between codes and their spectra for the systemconstitution in the second embodiment in a case where four userstransmit information signals, respectively, and each user only usescodes each made by repeating an auto-complementary sequence, and doesnot use cross-complementary sequences. This system constitution isrealized by replacing the spreading codes at transmitter 2 in FIG. 1from (B0, B0, B0, B0) to (A6, A6, A6, A6) and from (B1, B1, B1, B1) to(A7, A7, A7, A7), by replacing the carrier waves from (f0, f1) to (f6,f7), by replacing the carrier waves at receiver 4 from (f0, f1) to (f6,f7) and by replacing the codes of matched filters from (B0B0) to (A6A6)and from (B1B1) to (A7A7).

In FIG. 8, to simplify the illustration of the spectra, it is assumedthat each auto-complementary sequence is constituted by repeating a4-chip basic sequence eight times. For example, let us assume to usecodes A0=(1, 1, 1, −1) and A1=(1, −1, 1, 1). Consider there is a closerelation between the repeating number of sequences and the vacantfrequency component spacing in the spectrum. For simultaneoustransmission by four users so as not to overlap eight spectra, it isnecessary to repeat the auto-complementary sequence eight or more times.FIG. 8 shows the spectra for a case where the frequencies of the carrierwaves used by the respective user transmitters are selected as f0 to f7so that the spectra of respective codes each made by repeating anauto-complementary sequence eight times may not overlap with those ofone another.

As stated above, in the first embodiment of the CDMA communicationsystem according to the present invention, cross-complementary sequencesare used and therefore it is possible for the receiver side to identifythe transmitted waves separately without interference even if thespectra of transmitted waves of the users overlap. Therefore, frequencyutilization efficiency enhances. In the second embodiment, since thereis no condition that the codes assigned to the respective users shouldhave the relation of cross-complementary sequences, the degree offreedom for possible user codes increases. In this respect, the secondembodiment has advantage in that the number of codes to be assigned toeach user can be greater than that in the first embodiment. The secondembodiment is useful, in particular for a case where it is required toincrease the number of users. It is also possible to carry out thesecond embodiment in combination with the first embodiment.

As stated so far, according to the present invention, a system can beconstructed by using such a method that code sequences each made byrepeating an auto-complementary sequence a plurality of times are usedas the spreading codes and, if necessary further, a pair of codesequences having the relation of cross-complementary sequences with oneanother are assigned to each station (user) as addresses. Consequently,this systems is capable of avoiding the influence of interference waves,therefore, solving the near-far problem inherent to CDMA communicationsystems. Thus, it is not necessary to provide the transmission powercontrol function, thereby resulting in allowing simple systemconstitution. Besides, the present invention contributes greatly torealizing a CDMA communication system capable of easily separatingmulti-path signals due to the auto-correlation characteristics without aside lobe.

1. Comb-form spectrum communication method using repeated complementary sequence modulation, said method comprising: constituting a transmitting signal by assigning one set of N auto-complementary sequences to each user, where N is an integer equal to or higher than 2, summing N signals each of which is made by repeating one of said N auto-complementary sequences a plurality of times, modulating the repeated sequence with an individual carrier frequency so as to have comb-form spectrum without overlapping in frequency with the other said signals, and arranging said N respective signals having auto-complementary sequence characteristics to N pieces of comb-form spectra.
 2. The comb-form spectrum communication method using repeated complementary sequence modulation according to claim 1, wherein said transmitting signal is constituted by the steps of: preparing N shift carrier waves so that the K-th frequency is made by adding the inverted value fT of a symbol period T K-times to a reference frequency so as to prevent said N comb-form spectra from overlapping with one another, where K=0, 1, 2, . . . , N−1, and composing N signals each created by modulating said respective N shift carrier waves with repeated sequences which are made by repeating respective sequences of each set of N complementary sequences which have a relation of auto-complementary sequences.
 3. The comb-form spectrum communication method using repeated complementary sequence modulation according to claim 2, wherein said set of N auto-complementary sequences assigned to each user are constituted so that said set of N auto-complementary sequences assigned to each user is cross-complementary to a set of N auto-complementary sequences assigned to another user; and the carrier waves used by all the users are said N shift carrier waves.
 4. The comb-form spectrum communication method using repeated complementary sequence modulation according to claim 2, wherein for a case where said set of auto-complementary sequences assigned to each user are not cross-complementary to a set of sequences assigned to another user, said transmitting signals are constituted so that the complementary sequences assigned to each user modulate said shift carrier waves whose frequencies are different from those used by the other users.
 5. The comb-form spectrum communication method using repeated complementary sequence modulation according to one of claims 1 through 4, wherein at a receiver side of the system, N matched filters each matched to a part of a code made by repeating each sequence of said set of N auto-complementary sequences are arranged in parallel in accordance with said set of N auto-complementary sequences, and the transmitted information is detected based on a result obtained by adding the correlation outputs of said N matched filters.
 6. The comb-form spectrum communication method using repeated complementary sequence modulation according to one of claims 1 through 4, wherein pseudo-periodic sequences, such as obtained by copying the rear and front portions with multiple chips of a finite-length periodic sequence which is made by repeating each sequence of said set of N auto-complementary sequences, and thereby adding the copied portions to the outer front side and the outer rear side of said finite length periodic sequence respectively, are used as codes assigned to respective users; and matched filters, each matched to said finite length periodic sequence made before extending itself to said pseudo-frequency sequence, are used for demodulation at the receiver side.
 7. The comb-form spectrum communication method using repeated complementary sequence modulation wherein correlation outputs we obtained by using convolvers instead of said matched filters recited in claim
 5. 8. The comb-form spectrum communication method using repeated complementary sequence modulation wherein correlation outputs are obtained by using convolvers instead of said matched filters reciten in claim
 6. 